In order to facilitate relative rotation between the cage and its supporting surface, it is customary to provide the corresponding races with one or more radial bores opening onto the bearing surface thereof to enable the introduction of a lubricant such as oil at the interface between the race and the cage. With bearings rotating at high speeds, e.g. as part of a mechanism for oscillating a screen in the sifting of particulate matter, the centrifugal force tends to accumulate the lubricant along the inner surface of the outer race so that it will be convenient to use that surface for the guidance of the cage.
The machining and truing of the bearing surfaces can easily be done on the cast and hardened races by automatic means. Upon the drilling of the lubricating bore or bores in the outer race, however, the inner end of each bore has a burr which, since the bore registers with the contact surface of the cage, must be removed by painstaking reaming and refinishing operations that are time-consuming and expensive.